Method and apparatus for shuttle shifting a power transmission

Abstract

A method and apparatus for shuttle shifting a power transmission are disclosed. The transmission is of the type including a plurality of intermeshing gears and a plurality of clutches associated with the gears. The clutches are engageable in predetermined combinations to place the transmission in various gear ratios. A control system permits the transmission to be shuttle shifted from forward to reverse gear ratios and vice versa, taking into account the vehicle speed and the target gear ratio to be engaged following the shuttle shift. If the shuttle shift request prior to expiration of a preset time following movement of a command device from a directional position, the transmission is placed in a neutral condition. If the vehicle speed is greater than a maximum allowable shuttle shifting speed upon request of the shuttle shift, the transmission is placed in a neutral condition. If the speed is not greater than the maximum allowable shuttle shifting speed, a controller compares the target gear ratio to a maximum allowable shuttle shifting gear ratio and completes the shuttle shift in different manners depending upon a predetermined relationship between the gear ratios. When a shuttle shift is aborted by the vehicle operator, a ground speed matching control routine is executed in which a gear ratio most closely matching a ratio between the engine speed and the vehicle ground speed is engaged prior to resumption of the commanded gear ratio.

I claim: 
     
       1. A control system for a power transmission in a work vehicle, the transmission being of the type including a plurality of intermeshing gears and a plurality of clutches associated with the gears, the clutches being engageable and disengageable in predetermined combinations in response to control signals for establishing predetermined forward and reverse gear ratios between and input shaft and an output shaft of the transmission, the control system including: a sensor for detecting a parameter representative of vehicle speed;   a memory circuit for storing values representative of predetermined forward and reverse gear ratios, and of a reference vehicle speed;   an operator movable command device including a forward position for commanding the transmission to engage a forward gear ratio and a reverse position for commanding the transmission to engage a reverse gear ratio; and   a control circuit coupled to the sensor, the memory circuit and the command device, the control circuit being configured to monitor movement of the command device and to generate control signals for shifting the transmission to a neutral condition or between the predetermined forward and reverse gear ratios in response to movement of the command device between its forward and reverse positions based upon a predetermined relationship between the vehicle speed and the reference vehicle speed.   
     
     
       2. The control system of claim 1, wherein the transmission is shifted to a neutral condition when the command device is moved between its forward and reverse positions and the vehicle speed exceeds the reference vehicle speed. 
     
     
       3. The control system of claim 1, wherein the control circuit is configured to selectively shift the transmission to the neutral condition or between the predetermined forward and reverse gear ratios based upon a first reference vehicle speed when the command device is moved from its forward position to its reverse position and upon a second vehicle speed when the command device is moved from its reverse position to its forward position. 
     
     
       4. A control system for a power transmission in a work vehicle, the transmission being of the type including a plurality of intermeshing gears and a plurality of clutches associated with the gears, the clutches being engageable and disengageable in predetermined combinations in response to control signals for establishing predetermined forward and reverse gear ratios between and input shaft and an output shaft of the transmission, the control system including: a memory circuit for storing values representative of predetermined forward and reverse gear ratios and of a predetermined threshold gear ratio;   an operator movable command device including a forward position for commanding the transmission to engage the predetermined forward gear ratio and a reverse position for commanding the transmission to engage the predetermined reverse gear ratio; and   a control circuit coupled to the memory circuit and to the command device, the control circuit being configured to monitor movement of the command device between the forward and reverse positions and to generate control signals for shuttle shifting the transmission upon movement of the command device between the forward and reverse positions, the control circuit controlling shifting of the transmission in a first manner or a second manner based upon a predetermined relationship between the predetermined gear ratio to which the transmission is to be shifted and the threshold gear ratio.   
     
     
       5. The control system of claim 4, wherein the manner of shifting the transmission is based on a first threshold gear ratio for forward-to-reverse shuttle shifts and on a second threshold gear ratio for reverse-to-forward shuttle shifts. 
     
     
       6. The control system of claim 4, wherein for forward-to-reverse shuttle shifts, the predetermined reverse gear ratio is engaged when the predetermined reverse gear ratio does not exceed the threshold gear ratio, and the threshold gear ratio is engaged when the predetermined reverse gear ratio exceeds the threshold gear ratio. 
     
     
       7. The control system of claim 6, wherein when the predetermined reverse gear ratio exceeds the threshold ratio, the predetermined reverse gear ratio is set equal to the threshold gear ratio. 
     
     
       8. The control system of claim 4, wherein for reverse-to-forward shuttle shifts, the predetermined forward gear ratio is engaged when the predetermined forward gear ratio does not exceed the threshold gear ratio, and the threshold gear ratio is engaged when the predetermined forward gear ratio exceeds the threshold gear ratio. 
     
     
       9. The control system of claim 8, wherein following engagement of the threshold gear ratio, the control circuit is configured to shift the transmission from the threshold gear ratio to the predetermined gear ratio. 
     
     
       10. A control system for a power transmission in a work vehicle, the transmission being of the type including a plurality of intermeshing gears and a plurality of clutches associated with the gears, the clutches being engageable and disengageable in predetermined combinations in response to control signals for establishing predetermined forward and reverse gear ratios between and input shaft and an output shaft of the transmission, the control system including: a first sensor for detecting a first parameter representative of ground speed of the vehicle;   a second sensor for detecting a second parameter representative of engine output speed;   an operator movable command device including a forward position for commanding the transmission to engage the predetermined forward gear ratio and a reverse position for commanding the transmission to engage the predetermined reverse gear ratio; and   a control circuit coupled to the sensors and the command device, the control circuit being configured to monitor movement of the command device between the forward and reverse positions and to generate control signals for shuttle shifting the transmission between forward and reverse gear ratios in response to movement of the command device between the forward and reverse positions, and to execute a ground speed matching control routine to engage a gear ratio most closely matching a ratio between the first and second parameters when the command device is moved from the forward or the reverse position and back to the same position prior to completion of a shuttle shift.   
     
     
       11. The control system of claim 10, further including a memory circuit for storing values representative of predetermined forward and reverse gear ratios, wherein the control circuit is configured to shuttle shift the transmission between the predetermined gear ratios when the command device is moved between the forward and reverse positions. 
     
     
       12. The control system of claim 11, wherein following a shift to a ground speed matched gear ratio, the control circuit is further configured to shift the transmission to the predetermined gear ratio in its then current direction of travel. 
     
     
       13. A control system for a power transmission in a work vehicle, the transmission being of the type including a plurality of intermeshing gears and a plurality of clutches associated with the gears, the clutches being engageable and disengageable in predetermined combinations in response to control signals for establishing predetermined forward and reverse gear ratios between and input shaft and an output shaft of the transmission, the control system including: a memory circuit for storing values representative of predetermined forward and reverse gear ratios and of a predetermined threshold gear ratio;   an operator movable command device including first and second positions for commanding the transmission to engage the predetermined gear ratios; and   a control circuit coupled to the memory circuit and to the command device, the control circuit being configured to monitor movement of the command device between the first and second positions and to generate control signals for shuttle shifting the transmission upon movement of the command device between the first and second positions and for placing the transmission in a neutral condition when the command device is moved from the first position without entering the second position within a predetermined period of time.   
     
     
       14. The control system of claim 13, wherein after the predetermined period of time the control circuit is configured to command engagement of clutches for stopping rotation of an intermediate shaft of the transmission. 
     
     
       15. A method for shuttle shifting a power transmission between predetermined forward and reverse gear ratios, comprising the steps of: a) comparing a target gear ratio to be engaged following a shuttle shift to a threshold gear ratio;   b) executing the shuttle shift in a first manner when the target gear ratio and the threshold gear ratio satisfy a predetermined relationship and executing the shuttle shift in a second manner when the target gear and the threshold gear do not satisfy the predetermined relationship.   
     
     
       16. The method of claim 15, wherein the shuttle shift is a forward-to-reverse shuttle shift. 
     
     
       17. The method of claim 16, wherein the first manner includes shifting the transmission to the target gear ratio when the target gear ratio does not exceed the threshold gear ratio and the second manner includes shifting the transmission to the threshold gear ratio when the target gear ratio exceeds the threshold gear ratio. 
     
     
       18. The method of claim 15, wherein the shuttle shift is a reverse-to-forward shuttle shift. 
     
     
       19. The method of claim 18, wherein the first manner includes shifting the transmission to the target gear ratio when the target gear ratio does not exceed the threshold gear ratio and the second manner includes shifting the transmission to the threshold gear ratio when the target gear ratio exceeds the threshold gear ratio. 
     
     
       20. The method of claim 19, wherein when the target gear ratio exceeds the threshold gear ratio, the transmission is shifted to the target gear ratio following engagement of the threshold gear ratio. 
     
     
       21. A method for shifting a power shift transmission, comprising the steps of: a) monitoring movement of an operator movable shift command device from a first directional position;   b) shuttle shifting the transmission between predetermined forward and reverse gear ratios when the command device is moved from the first directional position to a second directional position opposite to the first directional position;   c) executing a ground speed matching control routine when the command device is moved back to the first directional position prior to completion of the shuttle shift, the ground speed matching control routine; and   d) engaging a ground speed matched gear ratio.   
     
     
       22. The method of claim 21, wherein the ground speed matching control routine executed at step c) includes determining a ground speed ratio between engine speed and a parameter proportional to vehicle speed and selecting a transmission gear ratio most closely matching the ground speed ratio. 
     
     
       23. The method of claim 21, wherein the ground speed matching control routine is executed when the command device is moved out of the first directional position and back to the first directional position without entering into a neutral position.